Magnetic field sensors are widely deployed in consumer and industrial instruments for applications varying from position sensing, current sensing, data storage, and magnetic compassing. There are many methods to sense magnetic fields including Hall-effect, magneto-diode, magneto-transistor, magnetoresistive-effect, magnetic tunnel junction, magneto-optical, fluxgate, search coil, and Lorentz force.
The Lorentz force resonant sensor fabricated by means of MEMS technology is preferred due to its low-cost batch fabrication technology. Lorentz force-effect resonant sensors are manufactured in a process flow similar to the process of motion sensors, such as accelerometers and gyroscopes. In addition, because Lorentz force-effect does not require special magnetic materials, it is the most compatible sensing mechanism for an integrated platform of motion sensors; magnetic field sensors, accelerometers, and gyroscopes. However, to detect a magnetic field as weak as the earth magnetic field, the magnetic field sensor is desired to have high sensitivity and low offset. High sensitivity is generally achieved by exciting at the resonant frequency and being packaged in vacuum for high quality factor. However, if the drive frequency is off by Δf from the resonant frequency, the sensitivity decreases significantly which proportional to Δf. In prior art, a close-loop frequency control system is needed to adjust the driving frequency dynamically to prevent significant sensitivity variation and the complicated close-loop control system could consume as high as 1 milliwatt per axis. In addition, the offset is generally larger than the signal and the offset variation limits the minimum detectable signal level. Thus, the design to mitigate offset is critical. Accordingly, what is needed is a system and method to address the above-identified issues. The present invention addresses such a need.